1. Field of the Invention
This invention relates a method of forming substrates and wafers of mercury cadmium telluride and to a method of forming narrow band gap substrates and wafers of mercury cadmium telluride wherein the band gap gradually increases in the region of the substrate or wafer surface.
2. Brief Description of the Prior Art
Mercury cadmium telluride substrates and wafers of the prior are formed wherein the mercury appears in an amount (1-x) and the cadmium appears in an amount x. Such substrates and wafers normally have value of x in the vicinity of about 0.2 to about 0.3. A problem that has been encountered in the devices formed in narrow band gap materials (x=0.2) is tunneling from the interface states due to the formation of oxide films or surface damage prior to device fabrication or the deposition of other insulating layers on the semiconductor surface. This problem can be mitigated in the prior art by increasing the band gap at the wafer or substrate surface from x=0.2 to x=0.3 or higher. Prior art techniques that have been used to perform this function are solidification techniques, growing of epitaxial films of different compositions directly on the surface of the substrate from tellurium-rich melts or mercury-rich melts and the like. These prior art methods have been relatively cumbersome and expensive and it is therefore desirable to provide a more efficient and/or less costly procedure for providing a graded increase in band gap toward the surface of the mercury cadmium telluride substrate or wafer.